A stop order is an order to buy or sell a stock once the price of the stock reaches a specified price, known as the stop price. When the specified price is reached, your stop order becomes a market order. The advantage of a stop order is you don't have to monitor how a stock is performing on a daily basis. The disadvantage is that a stop price purchase or sale could be activated by a short-term fluctuation in a stock's price. In addition, the price at which your trade is executed may differ from the stop price, especially in a fast-moving market where stock prices can change rapidly.